Perennial Streams

The Perennial Stream Mapping Project was initiated in September 2001 to
address concerns that perennial streams were not protected under the
county's Chesapeake Bay Preservation Ordinance, Chapter 118 of the
Fairfax County Code. At that time, the county's ordinance listed
perennial streams as those streams epicted as perennial on U.S.
Geological Survey topographical maps. In Fairfax County, a perennial
stream is defined as a body of water flowing in a natural or man-made
channel year-round, except during periods of drought. Those streams as
well as wetlands, tidal wetlands, and tidal shores were included within
Resource Protection Areas.

Streams not identified as perennial on U. S. Geological Survey maps
did not warrant a Resource Protection Area.

The Chesapeake Bay Local Assistance Department recognized difficulties
with the use of the U. S. Geological Survey maps. In December 2001, the
Chesapeake Bay Local Assistance Board adopted amendments to the state's
Chesapeake Bay Preservation Area Designation and Management
Regulations. The revised state regulations became effective on
March 1, 2002. The revisions include a requirement to perform
site-specific surveys using a scientifically valid method to identify
water bodies with perennial flow. The state regulations allow
localities some latitude in developing their own definition of
perennial streams and protocols for identifying them in the field.

Perennial Stream Mapping Project

To ensure compliance with the state's revised regulations, the county
has completed a Perennial Streams Mapping Project.

Fairfax County staff developed a Perennial
Stream Field Identification Protocol and Data
Sheet similar to the system used by North Carolina Division of
Water Quality. This protocol allowed Fairfax County staff to identify
perennial streams based on the combination of hydrological, physical
and biological characteristics of the stream. The field work was
completed between March 2002 and October 2003 and the new Resource
Protection Area maps were generated and approved by the Fairfax County
Board of Supervisors.

Report on Quality Control/Quality Assurance Methodology and Results

As part of the Perennial Streams Mapping Project, a Quality
Control/Quality Assurance study was conducted throughout 2004 to check
the accuracy and precision of the perennial stream determinations.

The following report presents the methodology and results of the
study, as well as recommendations and next steps.